Impaired baroreflex sensitivity as a potential marker of cardiovascular risk in hypertension.

Baroreflex heart rate control in hypertension Baroreflex mechanisms contribute importantly to shortterm regulation of heart rate, sympathetic tone and consequently blood pressure. The arterial baroreflex normally acts to oppose increases in blood pressure by inhibiting sympathetic activity, causing vasodilation and slowing heart rate. The traditional concept holds that arterial baroreflex is abnormal in hypertension [1,2], with a higher threshold for activation and a reduction in sensitivity; furthermore, these alterations result from chronic increases in arterial pressure. An important mechanism that allows sympathetic and arterial pressure to increase is baroreflex resetting [2]. Baroreflex resetting refers to a shift in the relationship between blood pressure changes and the efferent autonomic response (e.g. sympathetic nerve activity or heart rate). Sustained increases in pressure trigger a resetting of the operating point of the reflex to a higher level of pressure; that is, the baroreflex loses much of its ability to buffer the rise in pressure and actually functions to maintain pressure at the higher level. Hypertension-induced resetting of the baroreflex may be elicited by both ‘baroreceptor resetting’ (shift in pressure– afferent baroreflex activity relationship) and by ‘central resetting’ (shift in afferent baroreflex–efferent autonomic relationship) [3,4].